A need exists for superior sealing devices between sliding metal surfaces sealing fluid-containing compartments, especially when one or more of the fluids is corrosive or at an extreme temperature.
The typical sealing arrangement comprises a recess or groove in at least one of the surfaces, which recess is fitted with one or more separate sealing members adapted to be urged simultaneously against both surfaces desired to be sealed. When the surfaces slide with respect to each other, a sealing member contacting both surfaces must necessarily be exposed to sliding friction at its points of contact on at least one of the surfaces, yet the sealing function must not be impaired substantially.
Probably the most well-known seal of the type described is the elastomeric O-ring, so called because it is a ring of round cross-section. It is designed to fit in an annular groove in one of two mating cylindrical surfaces. It is deformable by pressure, and is made with inner and outer diameter such that it is substantially deformed by being squeezed between the groove in one surface and the mating surface. This arrangement provides for good sealing; however, the elastomeric materials in common use tend to be degraded by friction and corrosive chemicals. Further, most lose their desired physical properties when exposed to temperature extremes. If, instead, a seal is made of a relatively non-deformable material such as metal or synthetic resins, it may have superior resistance to friction and corrosion. However, it ordinarily lacks the ability to be urged into a tight contact over a surface area large enough to seal adequately, because of its relative non-deformability.
It has therefore been known to employ sealing systems which combine seals of both types of materials. See, for example, U.S. Pat. No. 2,739,855. In such systems, an elastomeric member is commonly used to provide the force which presses another material against the surfaces to be sealed.
The seal of the present invention is one such system. The seal combination is of the elastomer energized plastic type, in which the plastic is preferably PTFE (polytetrafluoroethylene). That is, it uses an elastomer to urge PTFE against a seal surface. In this way the low friction of PTFE can be employed to advantage, even though by itself PTFE lacks the elasticity to seal well. Such seals are known in the art. My preferred seal, however, enjoys certain advantages over prior seals. It is composed of two separate plastic rings and an elastomeric O-ring.
The plastic rings are shaped so as to partially surround the O-ring, which is sandwiched in between them. The plastic rings are provided with cantilevered lips which seal the surfaces on both sides of an additional seal provided by the O-ring.
This design makes possible the use of a standard O-ring, which is exposed only as a secondary seal to corrosive liquids. The three individual seal points on each side provide excellent protection from leakage. Moreover, the sandwiched arrangement permits the entrapment of lubricant which may be desired to be applied to the O-ring.
Accordingly, it is an object of the invention to provide improved means for sealing two cylindrical surfaces movable with respect to one another.
A further object of the invention is to provide such sealing means which remains effective under corrosive conditions.